As a heat-resistant member included in the engines for airplanes and the gas turbines for power generation, there is used a γ′ (gamma prime)-phase precipitation strengthening-type Ni-base super alloy which contains many alloy elements such as Al and Ti.
There has been used a forged alloy as an Ni-base super alloy in a turbine disk, among turbine components, which is required to have high strength and reliability. Here, the term “forged alloy” is used in comparison to a cast alloy which is used with a cast and solidified structure as it is. A forged alloy is a material which is manufactured by a process in which a steel ingot obtained by melting and solidification is subjected to hot working into a predetermined component shape. The hot working transforms a coarse, heterogeneous cast and solidified structure into a fine, uniform forged structure. This improves mechanical properties such as tensile strength and fatigue properties. In a low-pressure turbine disk for airplane engines, there is used an Ni-base super alloy including a γ′ phase as a strengthening phase, as disclosed in JP-A-2014-156660 (Patent Literature 1). However, in recent years, the turbine inlet temperature further increases due to the improvement in fuel consumption and efficiency, and the high temperature strength of a super alloy used is required to accordingly improve.